1. Field of the Invention
The present invention generally relates to an optical scanning device and an image forming apparatus employing the optical scanning device which is used for a laser printer, a laser facsimile, a digital copier, etc.
2. Description of the Related Art
It is general to write, by beam light (or laser beam) deflected by an optical scanning device, onto a photo conductor in an image forming apparatus according to an electrostatic photographic process in recent years correspondingly to digitization of an image forming apparatus. In the optical scanning device, it is necessary to carry out incidence of the beam light at a predetermined position on the photo conductor correctly.
For this purpose, to position correctly optical components thereof, such as various kinds of lenses, mirrors and so forth arranged inside the optical scanning device into an arrangement defined optically is demanded. Simultaneously, deformation of these components by stress, vibration, heat, etc. from the inside and outside of the optical scanning device must be prevented, and, thus, the beam light must be scanned correctly.
Furthermore, it is in the tendency to miniaturize the optical scanning device in an image forming apparatus from the request of the latest demand to save a space, and, for this purpose, it is necessary to bend the light path of beam light by several mirrors.
Such a space-saving optical scanning device should cause the beam light emitted from a beam light emitting device to pass through a cylindrical lens, make it reflected/deflected by a polygon mirror, and cause it to pass an fθ lens, cause the beam light to be bent by first and second mirrors which intersect perpendicularly mutually, and cause it to pass a long lens, and it is made to be reflected by a third mirror to the outside through a dust-proof glass. In addition, optical components, such as those lenses and mirrors, are arranged in predetermined positions, respectively, in a sealed optical box.
In the image forming apparatus equipped with such an optical scanning device, the beam light reflected to the outside by the third mirror is incident on the surface of a photo conductor, and, after forming of an electrostatic latent image on the rotating photo conductor by scanning the photo conductor with a straight line with rotation of the polygon mirror, a visible image is formed through a well-known electrophotographic image formation process.
FIG. 1 shows a sectional view showing an example in which an optical box of an optical scanning device is formed with resin by integral mold. FIG. 2 shows a perspective view of an essential part thereof, and other optical components than the fθ lens is omitted from indication there.
On a bottom surface 3a which is in a main surface of the optical box 3, an fθ lens receiving part 16 for positioning and fixing the fθ lens 9, a pair of first and second mirror receiving parts 17, 17 for positioning and fixing a first mirror 10, and a second mirror 11, a third mirror receiving part for positioning and fixing a third mirror 13, a long lens receiving part 19 for fixing a long lens 12 are formed integrally with the optical box 3, respectively.
A reference part for positioning is formed in each of these receiving parts, and, with a leaf spring or the like, each optical component is fixed to a respective positioning reference part by pressure (not shown). Thereby, the optical components, such as the above-mentioned lenses and mirrors are correctly arranged in the predetermined positions.
In the configuration of the optical box 3, under the fθ lens receiving part 16, an opening 3b is formed in the bottom surface 3a for allowing a moving mold to be inserted from the bottom in the integral molding process of the optical box 3, and, similarly, under the first and second mirror receiving parts 17, 17, openings 3c, 3c are formed in the bottom surface 3a for allowing the moving mold to be inserted from the bottom partially because receiving surfaces 17a, 17a for the second mirrors 11 are formed by under-cut in the molding process. Moreover, in the third minor receiving part 18, in order to secure a light path before and after the reflection by the third mirror 13, slit-like opening 18a is formed.
However, while having to prepare much opening parts in the bottom surface as mentioned above, therefore the rigidity of the optical box and vibration-proof nature thereof are degraded when integral molding of the optical box with resin is performed, and, also, in order to secure dust proof performance, covering members and seal members for closing these opening parts are needed.
Moreover, since most of these main optical components are directly arranged on the bottom surface of the optical box, there may be a possibility that the exact positional relationship between the respective optical components is degraded by uneven expansion/shrinkage of the optical box by change of environmental temperature, and degradation of plane nature of the bottom surface and deformation of the whole optical box due to aging factor, etc., thus, it may not be possible to maintain a stable optical performance.
In addition, due to a slight difference in length of a light path caused by a change in designed wavelength of the beam light, it is necessary to remake a metallic mold for molding the optical box which is a rather large-sized mold. Thereby, the time, effort and cost needed therefor may be remarkably large.